/*
** $Id: lgc.c,v 2.140 2013/03/16 21:10:18 roberto Exp $
** Garbage Collector
** See Copyright Notice in lua.h
*/

#include <string.h>

#define lgc_c
#define LUA_CORE

#include "lua.h"

#include "ldebug.h"
#include "ldo.h"
#include "lfunc.h"
#include "lgc.h"
#include "lmem.h"
#include "lobject.h"
#include "lstate.h"
#include "lstring.h"
#include "ltable.h"
#include "ltm.h"



/*
** cost of sweeping one element (the size of a small object divided
** by some adjust for the sweep speed)
*/
#define GCSWEEPCOST	((sizeof(TString) + 4) / 4)

/* maximum number of elements to sweep in each single step */
#define GCSWEEPMAX	(cast_int((GCSTEPSIZE / GCSWEEPCOST) / 4))

/* maximum number of finalizers to call in each GC step */
#define GCFINALIZENUM	4


/*
** macro to adjust 'stepmul': 'stepmul' is actually used like
** 'stepmul / STEPMULADJ' (value chosen by tests)
*/
#define STEPMULADJ		200


/*
** macro to adjust 'pause': 'pause' is actually used like
** 'pause / PAUSEADJ' (value chosen by tests)
*/
#define PAUSEADJ		100


/*
** 'makewhite' erases all color bits plus the old bit and then
** sets only the current white bit
*/
#define maskcolors	(~(bit2mask(BLACKBIT, OLDBIT) | WHITEBITS))
#define makewhite(g,x)	\
	(gch(x)->marked = cast_byte((gch(x)->marked & maskcolors) | luaC_white(g)))

#define white2gray(x)	resetbits(gch(x)->marked, WHITEBITS)
#define black2gray(x)	resetbit(gch(x)->marked, BLACKBIT)


#define isfinalized(x)		testbit(gch(x)->marked, FINALIZEDBIT)

#define checkdeadkey(n)	lua_assert(!ttisdeadkey(gkey(n)) || ttisnil(gval(n)))


#define checkconsistency(obj)  \
	lua_longassert(!iscollectable(obj) || righttt(obj))


#define markvalue(g,o) { checkconsistency(o); \
	if (valiswhite(o)) reallymarkobject(g,gcvalue(o)); }

#define markobject(g,t) { if ((t) && iswhite(obj2gco(t))) \
	reallymarkobject(g, obj2gco(t)); }

static void reallymarkobject (global_State *g, GCObject *o);


/*
** {======================================================
** Generic functions
** =======================================================
*/


/*
** one after last element in a hash array
*/
#define gnodelast(h)	gnode(h, cast(size_t, sizenode(h)))


/*
** link table 'h' into list pointed by 'p'
*/
#define linktable(h,p)	((h)->gclist = *(p), *(p) = obj2gco(h))


/*
** if key is not marked, mark its entry as dead (therefore removing it
** from the table)
*/
static void removeentry (Node *n) {
	lua_assert(ttisnil(gval(n)));
	if (valiswhite(gkey(n)))
		setdeadvalue(gkey(n));  /* unused and unmarked key; remove it */
}


/*
** tells whether a key or value can be cleared from a weak
** table. Non-collectable objects are never removed from weak
** tables. Strings behave as `values', so are never removed too. for
** other objects: if really collected, cannot keep them; for objects
** being finalized, keep them in keys, but not in values
*/
static int iscleared (global_State *g, const TValue *o) {
	if (!iscollectable(o)) return 0;
	else if (ttisstring(o)) {
		markobject(g, rawtsvalue(o));  /* strings are `values', so are never weak */
		return 0;
	}
	else return iswhite(gcvalue(o));
}


/*
** barrier that moves collector forward, that is, mark the white object
** being pointed by a black object.
*/
void luaC_barrier_ (lua_State *L, GCObject *o, GCObject *v) {
	global_State *g = G(L);
	lua_assert(isblack(o) && iswhite(v) && !isdead(g, v) && !isdead(g, o));
	lua_assert(g->gcstate != GCSpause);
	lua_assert(gch(o)->tt != LUA_TTABLE);
	if (keepinvariantout(g))  /* must keep invariant? */
		reallymarkobject(g, v);  /* restore invariant */
	else {  /* sweep phase */
		lua_assert(issweepphase(g));
		makewhite(g, o);  /* mark main obj. as white to avoid other barriers */
	}
}


/*
** barrier that moves collector backward, that is, mark the black object
** pointing to a white object as gray again. (Current implementation
** only works for tables; access to 'gclist' is not uniform across
** different types.)
*/
void luaC_barrierback_ (lua_State *L, GCObject *o) {
	global_State *g = G(L);
	lua_assert(isblack(o) && !isdead(g, o) && gch(o)->tt == LUA_TTABLE);
	black2gray(o);  /* make object gray (again) */
	gco2t(o)->gclist = g->grayagain;
	g->grayagain = o;
}


/*
** barrier for prototypes. When creating first closure (cache is
** NULL), use a forward barrier; this may be the only closure of the
** prototype (if it is a "regular" function, with a single instance)
** and the prototype may be big, so it is better to avoid traversing
** it again. Otherwise, use a backward barrier, to avoid marking all
** possible instances.
*/
LUAI_FUNC void luaC_barrierproto_ (lua_State *L, Proto *p, Closure *c) {
	global_State *g = G(L);
	lua_assert(isblack(obj2gco(p)));
	if (p->cache == NULL) {  /* first time? */
		luaC_objbarrier(L, p, c);
	}
	else {  /* use a backward barrier */
		black2gray(obj2gco(p));  /* make prototype gray (again) */
		p->gclist = g->grayagain;
		g->grayagain = obj2gco(p);
	}
}


/*
** check color (and invariants) for an upvalue that was closed,
** i.e., moved into the 'allgc' list
*/
void luaC_checkupvalcolor (global_State *g, UpVal *uv) {
	GCObject *o = obj2gco(uv);
	lua_assert(!isblack(o));  /* open upvalues are never black */
	if (isgray(o)) {
		if (keepinvariant(g)) {
			resetoldbit(o);  /* see MOVE OLD rule */
			gray2black(o);  /* it is being visited now */
			markvalue(g, uv->v);
		}
		else {
			lua_assert(issweepphase(g));
			makewhite(g, o);
		}
	}
}


/*
** create a new collectable object (with given type and size) and link
** it to '*list'. 'offset' tells how many bytes to allocate before the
** object itself (used only by states).
*/
GCObject *luaC_newobj (lua_State *L, int tt, size_t sz, GCObject **list,
					   int offset) {
						   global_State *g = G(L);
						   char *raw = cast(char *, luaM_newobject(L, novariant(tt), sz));
						   GCObject *o = obj2gco(raw + offset);
						   if (list == NULL)
							   list = &g->allgc;  /* standard list for collectable objects */
						   gch(o)->marked = luaC_white(g);
						   gch(o)->tt = tt;
						   gch(o)->next = *list;
						   *list = o;
						   return o;
}

/* }====================================================== */



/*
** {======================================================
** Mark functions
** =======================================================
*/


/*
** mark an object. Userdata, strings, and closed upvalues are visited
** and turned black here. Other objects are marked gray and added
** to appropriate list to be visited (and turned black) later. (Open
** upvalues are already linked in 'headuv' list.)
*/
static void reallymarkobject (global_State *g, GCObject *o) {
	lu_mem size;
	white2gray(o);
	switch (gch(o)->tt) {
	case LUA_TSHRSTR:
	case LUA_TLNGSTR: {
		size = sizestring(gco2ts(o));
		break;  /* nothing else to mark; make it black */
					  }
	case LUA_TUSERDATA: {
		Table *mt = gco2u(o)->metatable;
		markobject(g, mt);
		markobject(g, gco2u(o)->env);
		size = sizeudata(gco2u(o));
		break;
						}
	case LUA_TUPVAL: {
		UpVal *uv = gco2uv(o);
		markvalue(g, uv->v);
		if (uv->v != &uv->u.value)  /* open? */
			return;  /* open upvalues remain gray */
		size = sizeof(UpVal);
		break;
					 }
	case LUA_TLCL: {
		gco2lcl(o)->gclist = g->gray;
		g->gray = o;
		return;
				   }
	case LUA_TCCL: {
		gco2ccl(o)->gclist = g->gray;
		g->gray = o;
		return;
				   }
	case LUA_TTABLE: {
		linktable(gco2t(o), &g->gray);
		return;
					 }
	case LUA_TTHREAD: {
		gco2th(o)->gclist = g->gray;
		g->gray = o;
		return;
					  }
	case LUA_TPROTO: {
		gco2p(o)->gclist = g->gray;
		g->gray = o;
		return;
					 }
	default: lua_assert(0); return;
	}
	gray2black(o);
	g->GCmemtrav += size;
}


/*
** mark metamethods for basic types
*/
static void markmt (global_State *g) {
	int i;
	for (i=0; i < LUA_NUMTAGS; i++)
		markobject(g, g->mt[i]);
}


/*
** mark all objects in list of being-finalized
*/
static void markbeingfnz (global_State *g) {
	GCObject *o;
	for (o = g->tobefnz; o != NULL; o = gch(o)->next) {
		makewhite(g, o);
		reallymarkobject(g, o);
	}
}


/*
** mark all values stored in marked open upvalues. (See comment in
** 'lstate.h'.)
*/
static void remarkupvals (global_State *g) {
	UpVal *uv;
	for (uv = g->uvhead.u.l.next; uv != &g->uvhead; uv = uv->u.l.next) {
		if (isgray(obj2gco(uv)))
			markvalue(g, uv->v);
	}
}


/*
** mark root set and reset all gray lists, to start a new
** incremental (or full) collection
*/
static void restartcollection (global_State *g) {
	g->gray = g->grayagain = NULL;
	g->weak = g->allweak = g->ephemeron = NULL;
	markobject(g, g->mainthread);
	markvalue(g, &g->l_registry);
	markmt(g);
	markbeingfnz(g);  /* mark any finalizing object left from previous cycle */
}

/* }====================================================== */


/*
** {======================================================
** Traverse functions
** =======================================================
*/

static void traverseweakvalue (global_State *g, Table *h) {
	Node *n, *limit = gnodelast(h);
	/* if there is array part, assume it may have white values (do not
	traverse it just to check) */
	int hasclears = (h->sizearray > 0);
	for (n = gnode(h, 0); n < limit; n++) {
		checkdeadkey(n);
		if (ttisnil(gval(n)))  /* entry is empty? */
			removeentry(n);  /* remove it */
		else {
			lua_assert(!ttisnil(gkey(n)));
			markvalue(g, gkey(n));  /* mark key */
			if (!hasclears && iscleared(g, gval(n)))  /* is there a white value? */
				hasclears = 1;  /* table will have to be cleared */
		}
	}
	if (hasclears)
		linktable(h, &g->weak);  /* has to be cleared later */
	else  /* no white values */
		linktable(h, &g->grayagain);  /* no need to clean */
}


static int traverseephemeron (global_State *g, Table *h) {
	int marked = 0;  /* true if an object is marked in this traversal */
	int hasclears = 0;  /* true if table has white keys */
	int prop = 0;  /* true if table has entry "white-key -> white-value" */
	Node *n, *limit = gnodelast(h);
	int i;
	/* traverse array part (numeric keys are 'strong') */
	for (i = 0; i < h->sizearray; i++) {
		if (valiswhite(&h->array[i])) {
			marked = 1;
			reallymarkobject(g, gcvalue(&h->array[i]));
		}
	}
	/* traverse hash part */
	for (n = gnode(h, 0); n < limit; n++) {
		checkdeadkey(n);
		if (ttisnil(gval(n)))  /* entry is empty? */
			removeentry(n);  /* remove it */
		else if (iscleared(g, gkey(n))) {  /* key is not marked (yet)? */
			hasclears = 1;  /* table must be cleared */
			if (valiswhite(gval(n)))  /* value not marked yet? */
				prop = 1;  /* must propagate again */
		}
		else if (valiswhite(gval(n))) {  /* value not marked yet? */
			marked = 1;
			reallymarkobject(g, gcvalue(gval(n)));  /* mark it now */
		}
	}
	if (prop)
		linktable(h, &g->ephemeron);  /* have to propagate again */
	else if (hasclears)  /* does table have white keys? */
		linktable(h, &g->allweak);  /* may have to clean white keys */
	else  /* no white keys */
		linktable(h, &g->grayagain);  /* no need to clean */
	return marked;
}


static void traversestrongtable (global_State *g, Table *h) {
	Node *n, *limit = gnodelast(h);
	int i;
	for (i = 0; i < h->sizearray; i++)  /* traverse array part */
		markvalue(g, &h->array[i]);
	for (n = gnode(h, 0); n < limit; n++) {  /* traverse hash part */
		checkdeadkey(n);
		if (ttisnil(gval(n)))  /* entry is empty? */
			removeentry(n);  /* remove it */
		else {
			lua_assert(!ttisnil(gkey(n)));
			markvalue(g, gkey(n));  /* mark key */
			markvalue(g, gval(n));  /* mark value */
		}
	}
}


static lu_mem traversetable (global_State *g, Table *h) {
	const char *weakkey, *weakvalue;
	const TValue *mode = gfasttm(g, h->metatable, TM_MODE);
	markobject(g, h->metatable);
	if (mode && ttisstring(mode) &&  /* is there a weak mode? */
		((weakkey = strchr(svalue(mode), 'k')),
		(weakvalue = strchr(svalue(mode), 'v')),
		(weakkey || weakvalue))) {  /* is really weak? */
			black2gray(obj2gco(h));  /* keep table gray */
			if (!weakkey)  /* strong keys? */
				traverseweakvalue(g, h);
			else if (!weakvalue)  /* strong values? */
				traverseephemeron(g, h);
			else  /* all weak */
				linktable(h, &g->allweak);  /* nothing to traverse now */
	}
	else  /* not weak */
		traversestrongtable(g, h);
	return sizeof(Table) + sizeof(TValue) * h->sizearray +
		sizeof(Node) * cast(size_t, sizenode(h));
}


static int traverseproto (global_State *g, Proto *f) {
	int i;
	if (f->cache && iswhite(obj2gco(f->cache)))
		f->cache = NULL;  /* allow cache to be collected */
	markobject(g, f->source);
	for (i = 0; i < f->sizek; i++)  /* mark literals */
		markvalue(g, &f->k[i]);
	for (i = 0; i < f->sizeupvalues; i++)  /* mark upvalue names */
		markobject(g, f->upvalues[i].name);
	for (i = 0; i < f->sizep; i++)  /* mark nested protos */
		markobject(g, f->p[i]);
	for (i = 0; i < f->sizelocvars; i++)  /* mark local-variable names */
		markobject(g, f->locvars[i].varname);
	return sizeof(Proto) + sizeof(Instruction) * f->sizecode +
		sizeof(Proto *) * f->sizep +
		sizeof(TValue) * f->sizek +
		sizeof(int) * f->sizelineinfo +
		sizeof(LocVar) * f->sizelocvars +
		sizeof(Upvaldesc) * f->sizeupvalues;
}


static lu_mem traverseCclosure (global_State *g, CClosure *cl) {
	int i;
	for (i = 0; i < cl->nupvalues; i++)  /* mark its upvalues */
		markvalue(g, &cl->upvalue[i]);
	return sizeCclosure(cl->nupvalues);
}

static lu_mem traverseLclosure (global_State *g, LClosure *cl) {
	int i;
	markobject(g, cl->p);  /* mark its prototype */
	for (i = 0; i < cl->nupvalues; i++)  /* mark its upvalues */
		markobject(g, cl->upvals[i]);
	return sizeLclosure(cl->nupvalues);
}


static lu_mem traversestack (global_State *g, lua_State *th) {
	StkId o = th->stack;
	if (o == NULL)
		return 1;  /* stack not completely built yet */
	for (; o < th->top; o++)
		markvalue(g, o);
	if (g->gcstate == GCSatomic) {  /* final traversal? */
		StkId lim = th->stack + th->stacksize;  /* real end of stack */
		for (; o < lim; o++)  /* clear not-marked stack slice */
			setnilvalue(o);
	}
	return sizeof(lua_State) + sizeof(TValue) * th->stacksize;
}


/*
** traverse one gray object, turning it to black (except for threads,
** which are always gray).
*/
static void propagatemark (global_State *g) {
	lu_mem size;
	GCObject *o = g->gray;
	lua_assert(isgray(o));
	gray2black(o);
	switch (gch(o)->tt) {
	case LUA_TTABLE: {
		Table *h = gco2t(o);
		g->gray = h->gclist;  /* remove from 'gray' list */
		size = traversetable(g, h);
		break;
					 }
	case LUA_TLCL: {
		LClosure *cl = gco2lcl(o);
		g->gray = cl->gclist;  /* remove from 'gray' list */
		size = traverseLclosure(g, cl);
		break;
				   }
	case LUA_TCCL: {
		CClosure *cl = gco2ccl(o);
		g->gray = cl->gclist;  /* remove from 'gray' list */
		size = traverseCclosure(g, cl);
		break;
				   }
	case LUA_TTHREAD: {
		lua_State *th = gco2th(o);
		g->gray = th->gclist;  /* remove from 'gray' list */
		th->gclist = g->grayagain;
		g->grayagain = o;  /* insert into 'grayagain' list */
		black2gray(o);
		size = traversestack(g, th);
		break;
					  }
	case LUA_TPROTO: {
		Proto *p = gco2p(o);
		g->gray = p->gclist;  /* remove from 'gray' list */
		size = traverseproto(g, p);
		break;
					 }
	default: lua_assert(0); return;
	}
	g->GCmemtrav += size;
}


static void propagateall (global_State *g) {
	while (g->gray) propagatemark(g);
}


static void propagatelist (global_State *g, GCObject *l) {
	lua_assert(g->gray == NULL);  /* no grays left */
	g->gray = l;
	propagateall(g);  /* traverse all elements from 'l' */
}

/*
** retraverse all gray lists. Because tables may be reinserted in other
** lists when traversed, traverse the original lists to avoid traversing
** twice the same table (which is not wrong, but inefficient)
*/
static void retraversegrays (global_State *g) {
	GCObject *weak = g->weak;  /* save original lists */
	GCObject *grayagain = g->grayagain;
	GCObject *ephemeron = g->ephemeron;
	g->weak = g->grayagain = g->ephemeron = NULL;
	propagateall(g);  /* traverse main gray list */
	propagatelist(g, grayagain);
	propagatelist(g, weak);
	propagatelist(g, ephemeron);
}


static void convergeephemerons (global_State *g) {
	int changed;
	do {
		GCObject *w;
		GCObject *next = g->ephemeron;  /* get ephemeron list */
		g->ephemeron = NULL;  /* tables will return to this list when traversed */
		changed = 0;
		while ((w = next) != NULL) {
			next = gco2t(w)->gclist;
			if (traverseephemeron(g, gco2t(w))) {  /* traverse marked some value? */
				propagateall(g);  /* propagate changes */
				changed = 1;  /* will have to revisit all ephemeron tables */
			}
		}
	} while (changed);
}

/* }====================================================== */


/*
** {======================================================
** Sweep Functions
** =======================================================
*/


/*
** clear entries with unmarked keys from all weaktables in list 'l' up
** to element 'f'
*/
static void clearkeys (global_State *g, GCObject *l, GCObject *f) {
	for (; l != f; l = gco2t(l)->gclist) {
		Table *h = gco2t(l);
		Node *n, *limit = gnodelast(h);
		for (n = gnode(h, 0); n < limit; n++) {
			if (!ttisnil(gval(n)) && (iscleared(g, gkey(n)))) {
				setnilvalue(gval(n));  /* remove value ... */
				removeentry(n);  /* and remove entry from table */
			}
		}
	}
}


/*
** clear entries with unmarked values from all weaktables in list 'l' up
** to element 'f'
*/
static void clearvalues (global_State *g, GCObject *l, GCObject *f) {
	for (; l != f; l = gco2t(l)->gclist) {
		Table *h = gco2t(l);
		Node *n, *limit = gnodelast(h);
		int i;
		for (i = 0; i < h->sizearray; i++) {
			TValue *o = &h->array[i];
			if (iscleared(g, o))  /* value was collected? */
				setnilvalue(o);  /* remove value */
		}
		for (n = gnode(h, 0); n < limit; n++) {
			if (!ttisnil(gval(n)) && iscleared(g, gval(n))) {
				setnilvalue(gval(n));  /* remove value ... */
				removeentry(n);  /* and remove entry from table */
			}
		}
	}
}


static void freeobj (lua_State *L, GCObject *o) {
	switch (gch(o)->tt) {
	case LUA_TPROTO: luaF_freeproto(L, gco2p(o)); break;
	case LUA_TLCL: {
		luaM_freemem(L, o, sizeLclosure(gco2lcl(o)->nupvalues));
		break;
				   }
	case LUA_TCCL: {
		luaM_freemem(L, o, sizeCclosure(gco2ccl(o)->nupvalues));
		break;
				   }
	case LUA_TUPVAL: luaF_freeupval(L, gco2uv(o)); break;
	case LUA_TTABLE: luaH_free(L, gco2t(o)); break;
	case LUA_TTHREAD: luaE_freethread(L, gco2th(o)); break;
	case LUA_TUSERDATA: luaM_freemem(L, o, sizeudata(gco2u(o))); break;
	case LUA_TSHRSTR:
		G(L)->strt.nuse--;
		/* go through */
	case LUA_TLNGSTR: {
		luaM_freemem(L, o, sizestring(gco2ts(o)));
		break;
					  }
	default: lua_assert(0);
	}
}


#define sweepwholelist(L,p)	sweeplist(L,p,MAX_LUMEM)
static GCObject **sweeplist (lua_State *L, GCObject **p, lu_mem count);


/*
** sweep the (open) upvalues of a thread and resize its stack and
** list of call-info structures.
*/
static void sweepthread (lua_State *L, lua_State *L1) {
	if (L1->stack == NULL) return;  /* stack not completely built yet */
	sweepwholelist(L, &L1->openupval);  /* sweep open upvalues */
	luaE_freeCI(L1);  /* free extra CallInfo slots */
	/* should not change the stack during an emergency gc cycle */
	if (G(L)->gckind != KGC_EMERGENCY)
		luaD_shrinkstack(L1);
}


/*
** sweep at most 'count' elements from a list of GCObjects erasing dead
** objects, where a dead (not alive) object is one marked with the "old"
** (non current) white and not fixed.
** In non-generational mode, change all non-dead objects back to white,
** preparing for next collection cycle.
** In generational mode, keep black objects black, and also mark them as
** old; stop when hitting an old object, as all objects after that
** one will be old too.
** When object is a thread, sweep its list of open upvalues too.
*/
static GCObject **sweeplist (lua_State *L, GCObject **p, lu_mem count) {
	global_State *g = G(L);
	int ow = otherwhite(g);
	int toclear, toset;  /* bits to clear and to set in all live objects */
	int tostop;  /* stop sweep when this is true */
	if (isgenerational(g)) {  /* generational mode? */
		toclear = ~0;  /* clear nothing */
		toset = bitmask(OLDBIT);  /* set the old bit of all surviving objects */
		tostop = bitmask(OLDBIT);  /* do not sweep old generation */
	}
	else {  /* normal mode */
		toclear = maskcolors;  /* clear all color bits + old bit */
		toset = luaC_white(g);  /* make object white */
		tostop = 0;  /* do not stop */
	}
	while (*p != NULL && count-- > 0) {
		GCObject *curr = *p;
		int marked = gch(curr)->marked;
		if (isdeadm(ow, marked)) {  /* is 'curr' dead? */
			*p = gch(curr)->next;  /* remove 'curr' from list */
			freeobj(L, curr);  /* erase 'curr' */
		}
		else {
			if (testbits(marked, tostop))
				return NULL;  /* stop sweeping this list */
			if (gch(curr)->tt == LUA_TTHREAD)
				sweepthread(L, gco2th(curr));  /* sweep thread's upvalues */
			/* update marks */
			gch(curr)->marked = cast_byte((marked & toclear) | toset);
			p = &gch(curr)->next;  /* go to next element */
		}
	}
	return (*p == NULL) ? NULL : p;
}


/*
** sweep a list until a live object (or end of list)
*/
static GCObject **sweeptolive (lua_State *L, GCObject **p, int *n) {
	GCObject ** old = p;
	int i = 0;
	do {
		i++;
		p = sweeplist(L, p, 1);
	} while (p == old);
	if (n) *n += i;
	return p;
}

/* }====================================================== */


/*
** {======================================================
** Finalization
** =======================================================
*/

static void checkSizes (lua_State *L) {
	global_State *g = G(L);
	if (g->gckind != KGC_EMERGENCY) {  /* do not change sizes in emergency */
		int hs = g->strt.size / 2;  /* half the size of the string table */
		if (g->strt.nuse < cast(lu_int32, hs))  /* using less than that half? */
			luaS_resize(L, hs);  /* halve its size */
		luaZ_freebuffer(L, &g->buff);  /* free concatenation buffer */
	}
}


static GCObject *udata2finalize (global_State *g) {
	GCObject *o = g->tobefnz;  /* get first element */
	lua_assert(isfinalized(o));
	g->tobefnz = gch(o)->next;  /* remove it from 'tobefnz' list */
	gch(o)->next = g->allgc;  /* return it to 'allgc' list */
	g->allgc = o;
	resetbit(gch(o)->marked, SEPARATED);  /* mark that it is not in 'tobefnz' */
	lua_assert(!isold(o));  /* see MOVE OLD rule */
	if (!keepinvariantout(g))  /* not keeping invariant? */
		makewhite(g, o);  /* "sweep" object */
	return o;
}


static void dothecall (lua_State *L, void *ud) {
	UNUSED(ud);
	luaD_call(L, L->top - 2, 0, 0);
}


static void GCTM (lua_State *L, int propagateerrors) {
	global_State *g = G(L);
	const TValue *tm;
	TValue v;
	setgcovalue(L, &v, udata2finalize(g));
	tm = luaT_gettmbyobj(L, &v, TM_GC);
	if (tm != NULL && ttisfunction(tm)) {  /* is there a finalizer? */
		int status;
		lu_byte oldah = L->allowhook;
		int running  = g->gcrunning;
		L->allowhook = 0;  /* stop debug hooks during GC metamethod */
		g->gcrunning = 0;  /* avoid GC steps */
		setobj2s(L, L->top, tm);  /* push finalizer... */
		setobj2s(L, L->top + 1, &v);  /* ... and its argument */
		L->top += 2;  /* and (next line) call the finalizer */
		status = luaD_pcall(L, dothecall, NULL, savestack(L, L->top - 2), 0);
		L->allowhook = oldah;  /* restore hooks */
		g->gcrunning = running;  /* restore state */
		if (status != LUA_OK && propagateerrors) {  /* error while running __gc? */
			if (status == LUA_ERRRUN) {  /* is there an error object? */
				const char *msg = (ttisstring(L->top - 1))
					? svalue(L->top - 1)
					: "no message";
				luaO_pushfstring(L, "error in __gc metamethod (%s)", msg);
				status = LUA_ERRGCMM;  /* error in __gc metamethod */
			}
			luaD_throw(L, status);  /* re-throw error */
		}
	}
}


/*
** move all unreachable objects (or 'all' objects) that need
** finalization from list 'finobj' to list 'tobefnz' (to be finalized)
*/
static void separatetobefnz (lua_State *L, int all) {
	global_State *g = G(L);
	GCObject **p = &g->finobj;
	GCObject *curr;
	GCObject **lastnext = &g->tobefnz;
	/* find last 'next' field in 'tobefnz' list (to add elements in its end) */
	while (*lastnext != NULL)
		lastnext = &gch(*lastnext)->next;
	while ((curr = *p) != NULL) {  /* traverse all finalizable objects */
		lua_assert(!isfinalized(curr));
		lua_assert(testbit(gch(curr)->marked, SEPARATED));
		if (!(iswhite(curr) || all))  /* not being collected? */
			p = &gch(curr)->next;  /* don't bother with it */
		else {
			l_setbit(gch(curr)->marked, FINALIZEDBIT); /* won't be finalized again */
			*p = gch(curr)->next;  /* remove 'curr' from 'finobj' list */
			gch(curr)->next = *lastnext;  /* link at the end of 'tobefnz' list */
			*lastnext = curr;
			lastnext = &gch(curr)->next;
		}
	}
}


/*
** if object 'o' has a finalizer, remove it from 'allgc' list (must
** search the list to find it) and link it in 'finobj' list.
*/
void luaC_checkfinalizer (lua_State *L, GCObject *o, Table *mt) {
	global_State *g = G(L);
	if (testbit(gch(o)->marked, SEPARATED) || /* obj. is already separated... */
		isfinalized(o) ||                           /* ... or is finalized... */
		gfasttm(g, mt, TM_GC) == NULL)                /* or has no finalizer? */
		return;  /* nothing to be done */
	else {  /* move 'o' to 'finobj' list */
		GCObject **p;
		GCheader *ho = gch(o);
		if (g->sweepgc == &ho->next) {  /* avoid removing current sweep object */
			lua_assert(issweepphase(g));
			g->sweepgc = sweeptolive(L, g->sweepgc, NULL);
		}
		/* search for pointer pointing to 'o' */
		for (p = &g->allgc; *p != o; p = &gch(*p)->next) { /* empty */ }
		*p = ho->next;  /* remove 'o' from root list */
		ho->next = g->finobj;  /* link it in list 'finobj' */
		g->finobj = o;
		l_setbit(ho->marked, SEPARATED);  /* mark it as such */
		if (!keepinvariantout(g))  /* not keeping invariant? */
			makewhite(g, o);  /* "sweep" object */
		else
			resetoldbit(o);  /* see MOVE OLD rule */
	}
}

/* }====================================================== */


/*
** {======================================================
** GC control
** =======================================================
*/


/*
** set a reasonable "time" to wait before starting a new GC cycle;
** cycle will start when memory use hits threshold
*/
static void setpause (global_State *g, l_mem estimate) {
	l_mem debt, threshold;
	estimate = estimate / PAUSEADJ;  /* adjust 'estimate' */
	threshold = (g->gcpause < MAX_LMEM / estimate)  /* overflow? */
		? estimate * g->gcpause  /* no overflow */
		: MAX_LMEM;  /* overflow; truncate to maximum */
	debt = -cast(l_mem, threshold - gettotalbytes(g));
	luaE_setdebt(g, debt);
}


#define sweepphases  \
	(bitmask(GCSsweepstring) | bitmask(GCSsweepudata) | bitmask(GCSsweep))


/*
** enter first sweep phase (strings) and prepare pointers for other
** sweep phases.  The calls to 'sweeptolive' make pointers point to an
** object inside the list (instead of to the header), so that the real
** sweep do not need to skip objects created between "now" and the start
** of the real sweep.
** Returns how many objects it swept.
*/
static int entersweep (lua_State *L) {
	global_State *g = G(L);
	int n = 0;
	g->gcstate = GCSsweepstring;
	lua_assert(g->sweepgc == NULL && g->sweepfin == NULL);
	/* prepare to sweep strings, finalizable objects, and regular objects */
	g->sweepstrgc = 0;
	g->sweepfin = sweeptolive(L, &g->finobj, &n);
	g->sweepgc = sweeptolive(L, &g->allgc, &n);
	return n;
}


/*
** change GC mode
*/
void luaC_changemode (lua_State *L, int mode) {
	global_State *g = G(L);
	if (mode == g->gckind) return;  /* nothing to change */
	if (mode == KGC_GEN) {  /* change to generational mode */
		/* make sure gray lists are consistent */
		luaC_runtilstate(L, bitmask(GCSpropagate));
		g->GCestimate = gettotalbytes(g);
		g->gckind = KGC_GEN;
	}
	else {  /* change to incremental mode */
		/* sweep all objects to turn them back to white
		(as white has not changed, nothing extra will be collected) */
		g->gckind = KGC_NORMAL;
		entersweep(L);
		luaC_runtilstate(L, ~sweepphases);
	}
}


/*
** call all pending finalizers
*/
static void callallpendingfinalizers (lua_State *L, int propagateerrors) {
	global_State *g = G(L);
	while (g->tobefnz) {
		resetoldbit(g->tobefnz);
		GCTM(L, propagateerrors);
	}
}


void luaC_freeallobjects (lua_State *L) {
	global_State *g = G(L);
	int i;
	separatetobefnz(L, 1);  /* separate all objects with finalizers */
	lua_assert(g->finobj == NULL);
	callallpendingfinalizers(L, 0);
	g->currentwhite = WHITEBITS; /* this "white" makes all objects look dead */
	g->gckind = KGC_NORMAL;
	sweepwholelist(L, &g->finobj);  /* finalizers can create objs. in 'finobj' */
	sweepwholelist(L, &g->allgc);
	for (i = 0; i < g->strt.size; i++)  /* free all string lists */
		sweepwholelist(L, &g->strt.hash[i]);
	lua_assert(g->strt.nuse == 0);
}


static l_mem atomic (lua_State *L) {
	global_State *g = G(L);
	l_mem work = -cast(l_mem, g->GCmemtrav);  /* start counting work */
	GCObject *origweak, *origall;
	lua_assert(!iswhite(obj2gco(g->mainthread)));
	markobject(g, L);  /* mark running thread */
	/* registry and global metatables may be changed by API */
	markvalue(g, &g->l_registry);
	markmt(g);  /* mark basic metatables */
	/* remark occasional upvalues of (maybe) dead threads */
	remarkupvals(g);
	propagateall(g);  /* propagate changes */
	work += g->GCmemtrav;  /* stop counting (do not (re)count grays) */
	/* traverse objects caught by write barrier and by 'remarkupvals' */
	retraversegrays(g);
	work -= g->GCmemtrav;  /* restart counting */
	convergeephemerons(g);
	/* at this point, all strongly accessible objects are marked. */
	/* clear values from weak tables, before checking finalizers */
	clearvalues(g, g->weak, NULL);
	clearvalues(g, g->allweak, NULL);
	origweak = g->weak; origall = g->allweak;
	work += g->GCmemtrav;  /* stop counting (objects being finalized) */
	separatetobefnz(L, 0);  /* separate objects to be finalized */
	markbeingfnz(g);  /* mark objects that will be finalized */
	propagateall(g);  /* remark, to propagate `preserveness' */
	work -= g->GCmemtrav;  /* restart counting */
	convergeephemerons(g);
	/* at this point, all resurrected objects are marked. */
	/* remove dead objects from weak tables */
	clearkeys(g, g->ephemeron, NULL);  /* clear keys from all ephemeron tables */
	clearkeys(g, g->allweak, NULL);  /* clear keys from all allweak tables */
	/* clear values from resurrected weak tables */
	clearvalues(g, g->weak, origweak);
	clearvalues(g, g->allweak, origall);
	g->currentwhite = cast_byte(otherwhite(g));  /* flip current white */
	work += g->GCmemtrav;  /* complete counting */
	return work;  /* estimate of memory marked by 'atomic' */
}


static lu_mem singlestep (lua_State *L) {
	global_State *g = G(L);
	switch (g->gcstate) {
	case GCSpause: {
		/* start to count memory traversed */
		g->GCmemtrav = g->strt.size * sizeof(GCObject*);
		lua_assert(!isgenerational(g));
		restartcollection(g);
		g->gcstate = GCSpropagate;
		return g->GCmemtrav;
				   }
	case GCSpropagate: {
		if (g->gray) {
			lu_mem oldtrav = g->GCmemtrav;
			propagatemark(g);
			return g->GCmemtrav - oldtrav;  /* memory traversed in this step */
		}
		else {  /* no more `gray' objects */
			lu_mem work;
			int sw;
			g->gcstate = GCSatomic;  /* finish mark phase */
			g->GCestimate = g->GCmemtrav;  /* save what was counted */;
			work = atomic(L);  /* add what was traversed by 'atomic' */
			g->GCestimate += work;  /* estimate of total memory traversed */ 
			sw = entersweep(L);
			return work + sw * GCSWEEPCOST;
		}
					   }
	case GCSsweepstring: {
		int i;
		for (i = 0; i < GCSWEEPMAX && g->sweepstrgc + i < g->strt.size; i++)
			sweepwholelist(L, &g->strt.hash[g->sweepstrgc + i]);
		g->sweepstrgc += i;
		if (g->sweepstrgc >= g->strt.size)  /* no more strings to sweep? */
			g->gcstate = GCSsweepudata;
		return i * GCSWEEPCOST;
						 }
	case GCSsweepudata: {
		if (g->sweepfin) {
			g->sweepfin = sweeplist(L, g->sweepfin, GCSWEEPMAX);
			return GCSWEEPMAX*GCSWEEPCOST;
		}
		else {
			g->gcstate = GCSsweep;
			return 0;
		}
						}
	case GCSsweep: {
		if (g->sweepgc) {
			g->sweepgc = sweeplist(L, g->sweepgc, GCSWEEPMAX);
			return GCSWEEPMAX*GCSWEEPCOST;
		}
		else {
			/* sweep main thread */
			GCObject *mt = obj2gco(g->mainthread);
			sweeplist(L, &mt, 1);
			checkSizes(L);
			g->gcstate = GCSpause;  /* finish collection */
			return GCSWEEPCOST;
		}
				   }
	default: lua_assert(0); return 0;
	}
}


/*
** advances the garbage collector until it reaches a state allowed
** by 'statemask'
*/
void luaC_runtilstate (lua_State *L, int statesmask) {
	global_State *g = G(L);
	while (!testbit(statesmask, g->gcstate))
		singlestep(L);
}


static void generationalcollection (lua_State *L) {
	global_State *g = G(L);
	lua_assert(g->gcstate == GCSpropagate);
	if (g->GCestimate == 0) {  /* signal for another major collection? */
		luaC_fullgc(L, 0);  /* perform a full regular collection */
		g->GCestimate = gettotalbytes(g);  /* update control */
	}
	else {
		lu_mem estimate = g->GCestimate;
		luaC_runtilstate(L, bitmask(GCSpause));  /* run complete (minor) cycle */
		g->gcstate = GCSpropagate;  /* skip restart */
		if (gettotalbytes(g) > (estimate / 100) * g->gcmajorinc)
			g->GCestimate = 0;  /* signal for a major collection */
		else
			g->GCestimate = estimate;  /* keep estimate from last major coll. */

	}
	setpause(g, gettotalbytes(g));
	lua_assert(g->gcstate == GCSpropagate);
}


static void incstep (lua_State *L) {
	global_State *g = G(L);
	l_mem debt = g->GCdebt;
	int stepmul = g->gcstepmul;
	if (stepmul < 40) stepmul = 40;  /* avoid ridiculous low values (and 0) */
	/* convert debt from Kb to 'work units' (avoid zero debt and overflows) */
	debt = (debt / STEPMULADJ) + 1;
	debt = (debt < MAX_LMEM / stepmul) ? debt * stepmul : MAX_LMEM;
	do {  /* always perform at least one single step */
		lu_mem work = singlestep(L);  /* do some work */
		debt -= work;
	} while (debt > -GCSTEPSIZE && g->gcstate != GCSpause);
	if (g->gcstate == GCSpause)
		setpause(g, g->GCestimate);  /* pause until next cycle */
	else {
		debt = (debt / stepmul) * STEPMULADJ;  /* convert 'work units' to Kb */
		luaE_setdebt(g, debt);
	}
}


/*
** performs a basic GC step
*/
void luaC_forcestep (lua_State *L) {
	global_State *g = G(L);
	int i;
	if (isgenerational(g)) generationalcollection(L);
	else incstep(L);
	/* run a few finalizers (or all of them at the end of a collect cycle) */
	for (i = 0; g->tobefnz && (i < GCFINALIZENUM || g->gcstate == GCSpause); i++)
		GCTM(L, 1);  /* call one finalizer */
}


/*
** performs a basic GC step only if collector is running
*/
void luaC_step (lua_State *L) {
	global_State *g = G(L);
	if (g->gcrunning) luaC_forcestep(L);
	else luaE_setdebt(g, -GCSTEPSIZE);  /* avoid being called too often */
}



/*
** performs a full GC cycle; if "isemergency", does not call
** finalizers (which could change stack positions)
*/
void luaC_fullgc (lua_State *L, int isemergency) {
	global_State *g = G(L);
	int origkind = g->gckind;
	lua_assert(origkind != KGC_EMERGENCY);
	if (isemergency)  /* do not run finalizers during emergency GC */
		g->gckind = KGC_EMERGENCY;
	else {
		g->gckind = KGC_NORMAL;
		callallpendingfinalizers(L, 1);
	}
	if (keepinvariant(g)) {  /* may there be some black objects? */
		/* must sweep all objects to turn them back to white
		(as white has not changed, nothing will be collected) */
		entersweep(L);
	}
	/* finish any pending sweep phase to start a new cycle */
	luaC_runtilstate(L, bitmask(GCSpause));
	luaC_runtilstate(L, ~bitmask(GCSpause));  /* start new collection */
	luaC_runtilstate(L, bitmask(GCSpause));  /* run entire collection */
	if (origkind == KGC_GEN) {  /* generational mode? */
		/* generational mode must be kept in propagate phase */
		luaC_runtilstate(L, bitmask(GCSpropagate));
	}
	g->gckind = origkind;
	setpause(g, gettotalbytes(g));
	if (!isemergency)   /* do not run finalizers during emergency GC */
		callallpendingfinalizers(L, 1);
}

/* }====================================================== */


